I am rebuilding a new hard drive and Air Drop is missing
I am making a stab in the dark here, but I think what the OP is trying to communicate is that Air Drop is not present *IN THE SIDEBAR* of his Finder Windows anymore.
If that is the case, the Finder's Preferences will allow you to re-check having Air Drop be visible in the sidebar again.
Thank you, I installed Yosemite and all is well, I have 35 years experience MS and one year Apple. I am learning.